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You can use a simple U-tube manometer (has nothing to do with the video channel), also called liquid column.
LEDs and Lighting Class
If you want to know how to charge SLA batteries correctly download the panasonic manual and read it carefully and you will notice that most chargers don't work optimal.https://eu.industrial.panasonic.com/sites/default/...P.S. I would be happy to find a manual for charging LiFePo4 as good as this one.
3D Printing Class
Small Horizontal Panel Saw ...View Instructable »
Can you tell us the type and manufacturer of the LEDs you are using?